Variations in incidence of schistosomiasis in the highveld region of Zimbabwe.

An incidence study of Schistosoma haematobium and S. mansoni was carried out among 487 six--eleven-year old children attending schools situated in the highveld region of Zimbabwe from July 1982 to March 1984. Incidence of both schistosome species were very high and there were marked variations in incidence by locality. No significant differences in incidence were observed between the sexes or among three age groups considered. Incidence of S. haematobium exceeded by a significant amount (P less than 0.02) that found for S. mansoni and this may be attributed to the relative abundance of the two species of snail intermediate hosts transmitting the two schistosome species. Incidence of both S. haematobium and S. mansoni declined markedly from period I (July 1982 to March 1983) to period II (March 1983 to March 1984) and this situation was associated with poor rains during the study. Poor rains probably resulted in a decrease in human water contact with natural waters which may account for the decline in incidence. Incidence results were separated by month and showed that transmission of the two schistosome species was highly seasonal and the demonstration that transmission in summer (September-November) exceeded that found in winter (June-August) substantiate the findings of malacological studies carried out in the highveld region of Zimbabwe.